2. Field of the Invention
This invention relates generally to abrasion-resistive coatings and more particularly to such coatings used on gemstones, pearls, crystals, and metal jewelry to improve wear resistance on softer materials as well as impart color via various methods.
3. Description of the Prior Art
Coloration of gemstones has gained in popularity as a way to improve the color characteristics of natural stones with poor color, or to impart natural and synthetic stones with new and unique shades. The gemstone industry currently produces some specific shades via metal or metal oxide coatings, but such treatments are not robust and can get easily damaged by chemicals or by mechanical abrasion. Additionally the choice of coatings used for imparting color to the gemstone are limited to those that can be deposited to provide an adherent coating on the gemstone material. And although multilayer coatings using thin films is possible, stresses can easily lead to cracking, peeling and flaking of the coatings.
Currently, Tavalite® and Mystic Fire® brand topaz coatings use mixtures of metal oxides in a low pressure chemical vapor deposition (LPCVD) process to produce dichroic color patterns as in Tavalite and rainbow effect through vacuum deposition metal/metal oxide atoms as in Mystic Fire. In the case of Tavalite, the coating is present on both sides. In the case of Mystic Fire, the coating is present either on the pavilion side or on the crown side (called Nirvana topaz). These and other color coating treatments on gemstones can be easily damaged by scratching, exposure to abrasives, and chemicals (e.g. pickling solutions).
Other methods of color treatment include a form of sintering process. In the sintering process, the color imparting agent is in the form of a powder that is packed around the gemstone and thereafter exposed to elevated temperatures for long periods of time. In this process the coloring agent diffuses into the near-surface of the gemstone. A known drawback to the sintering method of colorization is that any damage to the gemstone such as scratches, dings, or abrasion will easily reveal the colorless gemstone material from behind.
In yet another form of color treatment, gemstones are irradiated with energetic beams to induce color centers. One drawback of this method, however, is that irradiated gemstones may lose their color over time when exposed to light.
Metal jewelry—such as that made with noble metals such as platinum or gold or other metals such as rhodium, titanium, tungsten, etc.—is susceptible to micro-scratches which greatly affect its appearance over time. These micro-scratches result from the general wear and tear caused by potential customers handling the jewelry in retail showrooms and subsequently wearing the jewelry, thereby causing the product to lose its finish and shine.
The prior art only teaches methods for producing specific colors to gemstones via metal or metal oxide coating depositions, diffusion treatments or irradiation. This resulting color, however, is susceptible to damage. Accordingly, the need remains for improved means and methods to impart colored or uncolored protective layers to gemstones, precious metal jewelry, and the like that do not decrease the decorative desirability of the object so protected.